Study on the oxidation and reduction of tungsten surface for sub-50 nm patterning process
(Color online) Tungsten line before and after the oxygen plasma ashing of the mask layer for tungsten line pattern at a high temperature (>400 K): (a)before the oxygen plasma ashing and (b) after the oxygen plasma ashing of the mask layer.
Surface change of tungsten layer after the exposure to oxygen plasma. (a) The sheet resistance change (delta Rs ) measured as a function of process temperature for 20 s of oxidation. (b) The tungsten oxide thickness measured as a function of process time at 300 and 520 K. The oxidation of tungsten was conducted with a microwave plasma-type carbon stripper (4800 Ws, 1 Torr, 9 slm O2).
Effect of (a) bias power, (b) source power, and (c) total oxygen flow rate on the PR ashing rate and the thickness of WOx formed on tungsten surface at a low temperature (300 K). The oxygen pressure was maintained at 15 mTorr, and the processing time was 20 s. When one of the parameters was varied, the parameters such as source power, bias power, and total flow rate were maintained at 1800 Ws, 100 Wb, and 900 sccm, respectively.
(Color online) Comparison of tungsten surface oxidation after the mask layer removal processing at different process temperatures. (Patterned wafer was treated in a solution, a mixture of NH4OH, CH3COOH, HF, and H2O, for 10 min). (a) Bare tungsten wafer after a high temperature plasma processing. (b) Bare tungsten wafer at a low-temperature plasma processing. (c) Patterned wafer at a high-temperature plasma processing. (d) Patterned wafer after a low temperature plasma processing. (a) and (c) were processed at 520 K using the microwave plasma system at the condition of 4800 Ws, 1 Torr, 9 slm of O2, and for 20 s. (b) and (d) were processed at 300 K using the ICP system at the condition of 1800 Ws, 15 mTorr, 900 sccm of O2 for 20 s.
(Color online) XPS narrow scan data of (a) W and (b) O after the oxidation of tungsten (i), after the reduction with 150 Wb of bias power (ii), and after the reduction with 300 Wb of bias power (iii). The wafer was processed with 800 Ws, 15 m Torr, 300 sccm of H2, and for 30 s at 300 K using theICP.
(Color online) Cross-sectional SEM images of tungsten line pattern (a) after the oxidation of tungsten and (b) after the reduction with a bias power after the oxidation. The tungsten line pattern was treated for 10 min in a solution (a mixture of NH4OH, CH3COOH, HF, and H2O) after the plasma processing.
Erosion and profile change of the mask underlayer with bias power (a) before the reduction, (b) after the reduction with 300 Wb of bias power, and (c) after the reduction with 500 Wb of bias power. Other process conditions are the same as those in Fig. 5.
WOx thickness remaining on tungsten substrate after the reduction by varying bias power and operating pressure. For the reduction process, an ICP system was used and the wafer was processed with 800 Ws, 15 mTorr, 300 sccm of H2, and for 30 s at a low temperature (300 K).
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